Inhibition of hepatic stellate cell collagen synthesis by N-(methylamino)isobutyric acid

Involvement of sodium-coupled neutral amino acid transporters (system A) in l-proline transport in the rat retinal pericytes

The retinal pericytes contribute to the supply of collagen to the basement membrane, and thus, form the structural support of the blood-retinal barrier. Since l-proline (L-Pro) is a major component of collagen, the uptake of L-Pro is an important process for the synthesis of collagen. This study was aimed to elucidate L-Pro transport mechanism(s) in the retinal pericytes. The transport of [³H]L-Pro was evaluated in the conditionally immortalized rat retinal pericyte cell line, TR-rPCT1 cells. The expression of the candidate transporter was examined by qualitative/quantitative reverse transcription-polymerase chain reaction, immunoblot analysis, and immunostaining. The [³H]L-Pro uptake by TR-rPCT1 cells showed Na⁺-dependence, Cl^--independence, and concentration-dependence with a K_m of 810 μM. The substrates for system A, such as 2-(methylamino)isobutyric acid (MeAIB), significantly inhibited the L-Pro uptake, suggesting the involvement of system A in the uptake of L-Pro. Among the subtypes of system A, the mRNA expression levels of ATA2 were the highest in TR-rPCT1 cells. Immunostaining analysis of the isolated rat retinal capillaries containing pericytes indicated the protein expression of ATA2 in retinal pericytes. In conclusion, it is suggested that ATA2, at least in part, is involved in the transport of L-Pro in the retinal pericytes.

Hypoxic preconditioning potentiates the trophic effects of mesenchymal stem cells on co-cultured human primary hepatocytes

Introduction

Mesenchymal stem/stromal cells (MSCs) improve the metabolic function of co-cultured hepatocytes. The present study aimed to further enhance the trophic effects of co-culture with hepatocytes using hypoxic preconditioning (HPc) of the MSCs and also to investigate the underlying molecular mechanisms involved.

Methods

Human adipose tissue-derived MSCs were subjected to hypoxia (2 % O₂; HPc) or normoxia (20 % O₂) for 24 h and then co-cultured with isolated human hepatocytes. Assays of metabolic function and apoptosis were performed to investigate the hepatotrophic and anti-apoptotic effects of co-culture. Indirect co-cultures and co-culture with MSC-conditioned medium investigated the role of paracrine factors in the hepatotrophic effects of co-culture. Reactive oxygen species (ROS) activity was antagonised with N-acetylcysteine to investigate whether HPc potentiated the effects of MSCs by intracellular ROS-dependent mechanisms. Tumour necrosis factor (TNF)-α, transforming growth factor (TGF)-β1, and extracellular collagen production was determined and CASP9 and BAX/BCL-2 signalling pathways analysed to investigate the role of soluble factors, extracellular matrix deposition, and apoptosis-associated gene signalling in the effects of co-culture.

Results

HPc potentiated the hepatotrophic and anti-apoptotic effects of co-culture by ROS-dependent mechanisms. There was increased MSC TGF-β1 production, and enhanced MSC deposition of extracellular collagen, with reduced synthesis of TNF-α, as well as a downregulation of the expression of pro-apoptotic CASP9, BAX, BID and BLK genes and upregulated expression of anti-apoptotic BCL-2 in hepatocytes.

Conclusions

HPc potentiated the trophic and anti-apoptotic effects of MSCs on hepatocytes via mechanisms including intracellular ROS, autocrine TGF-β, extracellular collagen and caspase and BAX/BCL-2 signalling pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0218-7) contains supplementary material, which is available to authorized users.

Adenosine A2A receptor occupancy stimulates collagen expression by hepatic stellate cells via pathways involving protein kinase A, Src, and extracellular signal-regulated kinases 1/2 signaling cascade or p38 mitogen-activated protein kinase signaling pathway

Prior studies indicate that adenosine and the adenosine A2A receptor play a role in hepatic fibrosis by a mechanism that has been proposed to involve direct stimulation of hepatic stellate cells (HSCs). The objective of this study was to determine whether primary hepatic stellate cells produce collagen in response to adenosine (via activation of adenosine A2A receptors) and to further determine the signaling mechanisms involved in adenosine A2A receptor-mediated promotion of collagen production. Cultured primary HSCs increase their collagen production after stimulation of the adenosine A2A receptor in a dose-dependent fashion. Likewise, LX-2 cells, a human HSC line, increases expression of procollagen alphaI and procollagen alphaIII mRNA and their translational proteins, collagen type I and type III, in response to pharmacological stimulation of adenosine A2A receptors. Based on the use of pharmacological inhibitors of signal transduction, adenosine A2A receptor-mediated stimulation of procollagen alphaI mRNA and collagen type I collagen expression were regulated by signal transduction involving protein kinase A, src, and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (erk), but surprisingly, adenosine A2A receptor-mediated stimulation of procollagen alphaIII mRNA and collagen type III protein expression depend on the activation of p38 mitogen-activated protein kinase (MAPK), findings confirmed by small interfering RNA-mediated knockdown of src, erk1, erk2, and p38 MAPK. These results indicate that adenosine A2A receptors signal for increased collagen production by multiple signaling pathways. These results provide strong evidence in support of the hypothesis that adenosine receptors promote hepatic fibrosis, at least in part, via direct stimulation of collagen expression and that signaling for collagen production proceeds via multiple pathways.

N-(methylamino)isobutyric acid inhibits proliferation of CFSC-2C hepatic stellate cells

Activation of hepatic stellate cells (HSCs) involves the induction of ECM protein synthesis and rapid cell proliferation. Thus, agents that interfere with either process could potentially mitigate the development of liver disease by reducing the synthesis of proteins associated with fibrosis or by reducing the number of activated HSC. Previously, we described that the non-metabolizable amino acid analog N-(methylamino)isobutyric acid (MeAIB) reduced hepatic collagen content of rats in a model of CCl(4)-induced liver injury, and in vitro studies using CFSC-2G cells indicated that MeAIB directly reduced collagen synthesis. However, the MeAIB-mediated reduction of hepatic collagen, in vivo, following liver injury was associated with a decrease in hepatic alpha-smooth muscle actin (alpha-SMA) which suggested that MeAIB also inhibited the activation of HSCs. Because HSC activation is inseparable from proliferation, the purpose of this study was to examine the effect of MeAIB treatment on the proliferation of HSCs in an in vitro model utilizing CFSC-2G cell cultures. In these studies, MeAIB effectively inhibited the proliferation of CFSC-2G cells by interfering with the progression of the cells through the G(1)-phase of the cell cycle which delayed entry into S-phase. MeAIB prevented the phosphorylation of p70S6 kinase (p70S6K) at Thr389 and reduced the phosphorylation at Thr421/Ser424. Because p70S6K is required for G(1)-cell cycle progression and is known to be regulated by nutrient availability, this correlates well with MeAIB interfering with the proliferation of CFSC-2G HSCs. In addition, the rate of protein synthesis was reduced by MeAIB treatment following mitogenic stimulation, which agrees with a p70S6K-mediated reduction in translation. These data are consistent with MeAIB inhibiting the proliferation of CFSC-2G cells by altering the mitogen activated pathway(s) leading to phosphorylation of p70S6K by a yet to be described mechanism.

Smad4 antisense gene transfer into ito cells and suppressed extracellular matrix production

AIM

To investigate possible role of antisense Smad4 RNA in the regulation of Smad4 and ECM production in Ito cells after blockade of TGF-β1 signal transmission by antisense Smad4.

METHODS

A rat Smad4 cDNA (2.5 kb) was inserted in reverse orientation into the adenoviral shuttle vector pAdv5SR (+), and so pAdvATSmad4 was obtained. PAdvATSmad4 was transfected, together with pJM17, into 293 cells by a liposome-mediated technique. We acquired the recombinant virus (AdvATSmad4) containing the anti-Smad4 gene by PCR detecting method. AdvATSmad4 was amplified and purified and then introduced into the rat Ito cell line CFSC.

RESULTS

The presence of antisense Smad4 RNA was detected by RT-PCR. The expression of Smad4 and the production of extracellular matrix were markedly decreased in the antisense Smad4 transfected cultured cells by in situ hybridization and immunohistochemistry.

CONCLUSION

Antisense RNA of Smad4 can be used successfully to inhibit Ito cell activation, endogenous Smad4 mRNA and extracellular matrix production, and may provide a basis for the development of anti-fibrosis gene therapy.